Required information Membrane Fluidity Cell membranes must maintain the right degree of fluidity for a cell to function correctly - not too fluid and not too solid. As temperature changes, a membrane transitions between a more fluid or a more solid state. Explore this interactive graph to discover how the molecular properties of lipids play a key role in determining the fluidity of the membrane at a given temperature. For one or two membranes, choose the number of carbon atoms in the lipid molecules, whether they are saturated or unsaturated, and whether cholesterol is present. Click the Plot the Graph button to see how these factors determine the transition temperature at which the membrane shifts from a more fluid to a more solid state. Click the Membrane Model tab for visual representations that help us understand the molecular basis of these relationships. Membrane Fluidity: Length of carbon tails and saturation levels Membrane fluidity depends on the length of the carbon tails in the phospholipid molecules and the presence or absence of double bonds. In theractive, use the drag bars to change the lengths of the carbon tails in the phospholipids and toggle on and off the presence of double bonds (saturation vs. unsaturation). Then assess the transition temperatures (Tm) of membranes composed of the following phospholipid molecules and select the two that have the most similar transition temperatures. Check All That Apply A phospholipid with 14 carbons and 0 double bonds A phospholipid with 14 carbons and 1 double bond A phospholipid with 20 carbons and 0 double bonds A phospholipid with 24 carbons and 1 double bond